Portable drug delivery devices are generally known for the administration of a medicinal substance or fluid, for example insulin, growth hormones or other drugs, being suitable for self-administration by a patient. A drug delivery device is especially useful in the shape of a pen, which can be handled easily and kept everywhere available. A sophisticated type of drug delivery device is constructed to be refillable and reusable many times. To secure a long life of the device, it is important to avoid damages caused during every day use.
Some drug delivery devices are constructed to deliver a plurality of different doses. One particular example of such a drug delivery device is described in EP1923083A1. The drug delivery device shown therein allows a user to activate the delivery device. For that purpose, the drug delivery device includes a drive mechanism suitable for use in pen-type injectors, where an amount of pre-set doses of a medicinal product can be administered. A needle unit can be attached to the drug delivery device for dispensing the medicinal product into a patient's body.
Necessary information about the drug delivery, the dosage or the particular drugs contained in the drug delivery device should be directly accessible by the user of the device and should therefore be visual on the body of the device. Further, with respect to patients using two different types of drugs it is helpful, if the patient has one device (for example one pen) for one type of drug and another device (for example pen) for the other type of drug. To avoid a mix-up between the two drugs, it is necessary to make the drug delivery devices distinguishable.